Smoking cessation telephone quitlines are an integral component in the US tobacco control program. But increasing their success is greatly needed. Even with quitlines' standard intervention of traditional Cognitive Behavioral Therapy combined with pharmacotherapy (typically nicotine replacement therapy; NRT), an average of 86% of smokers using quitlines will relapse to smoking (i.e., 14% stay quit). There are no new, proven-effective counseling approaches to improve the smoking cessation success rates of quitlines. We address this critical need by pilot testing a promising approach, called Acceptance & Commitment Therapy (ACT), as a telephone-delivered smoking cessation intervention. We recently completed a small (n =14) single- arm feasibility study of community-recruited participants which demonstrated that ACT for smoking cessation was feasibly-delivered by telephone and that participants were receptive to the intervention. At 12 months post- treatment (93% retention), the intent-to-treat prolonged abstinence rate was 29%. While results were promising, there was no control group, the sample size was only 14, participants were not quitline callers, and no NRT was provided. To build on these results, a pilot randomized controlled trial that includes a larger sample size, recruitment from quitline callers, and NRT provision is now needed to inform the design of a full- scale R01 randomized trial. Accordingly, the aims of this proposal are to conduct a pilot randomized trial comparing telephone-delivered ACT counseling plus NRT to telephone-delivered CBT counseling plus NRT, in order to: (1) Demonstrate that ACT's implementation outcomes are at least as good as those of traditional CBT; (2) Demonstrate that ACT, as compared to CBT, has a trend toward higher smoking cessation and related behavior change rates; (3) Demonstrate that the smoking cessation outcomes of ACT, but not traditional CBT, are mediated by two psychological measures that are central to the theoretical model underlying ACT: (a) acceptance of internal cues to smoke (sensations, emotions, and thoughts) and (b) commitment to quitting smoking. The key innovation is a new conceptual model for quitline counseling. The study applies this new model to the highly important public health problem of smoking cessation and tests the model in the widely disseminable context of a quitline. The study proposes a research paradigm shift toward increasing innovations in quitline counseling content. The proposal shows exciting promise for improving the success rates of quitlines and thereby lowering healthcare costs and reducing premature tobacco-related deaths. PUBLIC HEALTH RELEVANCE: This two-year R21 randomized trial will pilot test a newly emerging counseling approach, called Acceptance & Commitment Therapy (ACT), as a telephone-delivered smoking cessation intervention. If ACT is later proven effective in a full-scale trial and disseminated to 50% to 100% of US quitlines, it is possible that 31,000 to 61,000 more smokers could quit each year.